The conventional vacuum arc degassing system enables a user to lower oxygen and hydrogen contents of molten steel to low levels by the use of a sub-atmospheric pressure (or vacuum) which may be as low as less than 1 mm Hg if flake free hydrogen levels in large sections are desired, an alternating current electric arc which is struck directly between the AC electrodes and the molten steel, and inert gas purging. A typical example can be seen from U.S. Pat. No. 3,501,289 with respect to which the present invention is a further development. Almost invariably, the vacuum in this system, known as the vacuum arc degassing system, is generated by a plurality of steam jet ejectors and it requires, in the United States at least, licensed boiler tenders to operate. Also, in the vast majority of commercial installations, the inert gas purging is derived from, preferably, one or, at most, two porous bricks, each of which admits from 3-5 cu. ft./min. of purging gas to the molten steel. In some instances a tuyere which produces the same stirring characteristics, or even a porous bottom, may be substituted for the purging brick.
Such a system is relatively expensive to build since the steam jet ejector system is relatively expensive. Further, such a system is relatively costly to operate due to operators licensing requirements. It has however gained wide acceptance due to the ability to achieve the desired low gas results, as well as many other now well recognized advantages over prior systems including temperature and chemical homogenization, concast applications and others.
It is highly desirable however that the art have access to a system which achieves all, or substantially all, of the advantages of the vacuum arc degassing system but at a lower equipment and operating cost and is simpler to operate.